The goal of this project is to investigate the nature and specificity of the immune response that protects resistance mice from Theiler's murine encephalomyelitis virus (TMEV) persistent infection but which may also contribute in susceptible mice to demyelination and neurologic deficits. In this murine model of multiple sclerosis the immune system functions both to clear virus infection but also to exacerbate the pathogenic response which mediates myelin and axonal injury. The hypothesis to be tested is that antigens encoded by the TMEV genome are critical for protective immunity (resistance) but possibility may also contribute to immunopathology (susceptibility). The experiments will utilize a series of transgenic mice expressing independent three continuous regions of the TMEV genome. Transgenic mice have been created under control of a class I continuous regions of the TMEV genome. Transgenic mice have been created under control of a class I promoter expressing region I coding sequence 5' of VP1 (L, VP4, VP2, and VP3), region II (VP1 coding block), and region III coding sequence 3' of VP1 92A, 2B, 2C, 3A, 3B, 3C, and 3D). By challenging mice expressing TMEV transgenes with infectious virus, we will be able to address the role of immune response to TMEV coding regions in vivo. These experiments will also evaluate demyelination and neurologic deficits in transgenic mice expressing human class II MHC genes infected with TMEV. Finally we will study the phenotype and specificity of the immune response contributing to neurologic deficits utilizing adoptive transfer experiments with perforin deficient mice when injected with TMEV show demyelination but fail to show neurologic deficits. The experiments are expected to provide unique insights into the mechanisms of myelin injury and neurologic deficits with relevance to human multiple sclerosis.